1. Field of the Invention
The present invention relates to a magnetoresistive thin film head for use in, for example, a magnetic recording/reproducing device, such as, a magnetic disk unit.
2. Description of the Prior Art
A magnetoresistive thin film head (hereinafter also referred to as "MR head"), which is capable of reading out data recorded on a magnetic recording medium, such as, a magnetic disk, has been known as disclosed in, such as, Japanese Unexamined Patent Publication No. 2-68706.
FIG. 9 is a schematic partial front view showing a main portion of a conventional MR head. In FIG. 9, the MR head includes a substrate 1, and further includes an insulating film or layer 30, a shield film or layer 3, an insulating film or layer 31, a magnetoresistive element layer (hereinafter also referred to as "MR element layer") 5, lead films or layers 6-A and 6-B, an insulating film or layer 32 and a shield film or layer 8 which are stacked on the substrate 1 in the order named.
FIG. 10 is a schematic partial plan view showing the MR element layer 5 and the lead layers 6-A and 6-B. In FIG. 10, the lead layers 6-A and 6-B are connected to opposite ends of the MR element layer 5 of a rectangular shape, respectively.
FIG. 11 is a diagram showing the MR element layer 5 and the lead layers 6-A and 6-B in more detail. In FIG. 11, the MR element layer 5 is formed by a soft magnetic bias film or layer 10, a nonmagnetic intermediate spacer film or layer 11 and a magnetoresistive film or layer 12 formed of a material showing a magnetoresistance effect. The soft magnetic bias layer 10 is provided for applying a bias magnetic field to the magnetoresistive layer 12, the nonmagnetic intermediate spacer layer 11 is provided for magnetically separating the soft magnetic bias layer 10 and the magnetoresistive layer 12 from each other, and the magnetoresistive layer 12 is provided for converting a magnetic flux variation to an electrical signal.
The lead layers 6-A and 6-B are the same in structure with each other, each being formed by an antiferromagnetic bias film or layer 13, an adhesion strengthening film or layer 14 and a conductive lead film or layer 15. The antiferromagnetic bias layer 13 is provided for applying a magnetic exchange bias to an upper side of the magnetoresistive layer 12 in a flow direction of an energization current or a sense current.
Operations of the foregoing conventional MR head will be described hereinbelow.
When the sense current flows from the lead layer 6-A to the lead layer 6-B via the MR element layer 5, which then returns to a power supply, a magnetic field is generated in a direction perpendicular to the flow direction of the sense current due to the sense current flowing in the MR element layer 5. Accordingly, the magnetoresistive layer 12 and the soft magnetic bias layer 10 are magnetized such that the magnetization in the magnetoresistive layer 12 is biased or directed in a direction perpendicular to the flow direction of the sense current due to an effect of coupling between the magnetoresistive layer 12 and the soft magnetic bias layer 10.
When an external magnetic field is applied to the biased magnetoresistive layer 12, the magnetoresistive layer 12 linearly changes its electric resistance depending on a variation of the applied external magnetic field so that, by processing this resistance variation of the magnetoresistive layer 12 as an electrical signal, a required output can be reliably attained, that is, a magnetic field recorded on the magnetic recording medium representing the recorded magnetic data on the magnetic recording medium can be read out reliably.
Since, as described above, the magnetoresistive layer 12 of the MR element layer 5 works as an electric resistor, the MR element layer 5 is heated due to the sense current flowing through the magnetoresistive layer 12. The generated heat is radiated to the shield layers 3, 8 and to the substrate 1 via the lead layers 6-A and 6-B and the insulating layers 30, 31 and 32.
As described above, in order to operate the MR head, it is necessary that the sense current be arranged to flow in the MR element layer 5. An allowable maximum value of the sense current is determined in view of durability of the MR element layer 5 when being energized. Specifically, since a thickness of the MR element layer 5 is normally only no more than 0.1 .mu.m, even a slight heating value causes the MR element layer 5 to be fused, leading to rupture of the MR head.
In order to avoid such an incident, it is necessary to reduce the heating value to be generated or improve the heat radiation effect.
In the conventional MR head, however, the heat radiation effect is poor due to a material forming the insulating layers so that the MR element layer 5 is likely to be damaged even with the slight heating value, and thus, an allowable maximum value of the sense current should be inevitably set small. Since the MR element layer 5 is subject to breakage when the sense current over this small allowable maximum value flows therethrough, the conventional MR head is defective in view of reliability.